1. Field of the Invention
The present invention relates to a circuit breaker used for a power transmission line or a power distribution line, and in particular to an interrupter for a circuit breaker which can distribute and weaken an arc resulting from separation of contacts, can reduce loss of the contacts by the arc, and can improve interruption performance, in case an abnormal current, such as an overcurrent is generated, by providing a movable electrode and a fixed electrode which can form a plurality of vertical magnetic fields in parallel with a generation direction of the arc.
2. Description of the Background Art
In general, a circuit breaker is employed in a power transmission line, a power distribution line or independent transformation facilities of electrical energy in order to protect devices at a load side, such as an electric transformer or a motor from an abnormal current. The circuit breaker must be provided with high breaking performance, safety and reliability.
In an atmosphere in a container having an interrupter, the circuit breaker is classified into an oil circuit breaker using oil, a gas-insulated circuit breaker employing SF.sub.6, an air insulated circuit breaker using air, a magnetic blow-out circuit breaker utilizing a magnetic field, and a vacuum circuit breaker using a good insulation property and a rapid arc extinguishing operation in a vacuum atmosphere.
Among these circuit breakers, the vacuum circuit breaker has a superior insulation recovery property. Since the vacuum circuit breaker was manufactured in the 1960s to open/close a contact in a vacuum, it has achieved high voltage, large current operation and a small size.
The interrupter which is a major constitutional component of the vacuum circuit breaker is provided with two electrodes respectively having a contact connected to each other in an insulated container hermetically sealed in order to maintain a vacuum state.
One of the two electrodes is connected to a trip mechanism operated by a trip signal of a control circuit sensing the abnormal current, and to a link connected to the trip mechanism, and thus is operated separately from the other electrode with their contacts connected.
The electrodes of the interrupter tend to be easily melted and hardened by the arc generated when the contacts are separated. Accordingly, there is a need for improving a melting and hardening resistance property.
A spiral or helix contact or a contrate contact has been fabricated, in order to improve the melting and hardening resistance property of the contact composing the electrode of the interrupter. The contact is prevented from being melted and hardened due to concentration of the arc by applying a magnetic field which is perpendicular (horizontal direction) to the arc generated when the abnormal current is interrupted, and by moving the arc in the horizontal direction.
An example of the conventional interrupter electrode structure composing the circuit breaker will now be described with reference to the accompanying drawings.
FIG. 1 illustrates a turn-off state of the conventional interrupter having the spiral contact. The interrupter includes an insulated container 10 formed in a cylindrical shape, and maintaining a vacuum state having its both end portions welded with covers 20, 21; and a fixed electrode 30 and a movable electrode 40 respectively, having contacts 31, 41 symmetrically arranged in the insulated container 10, and connected with or separated from each other, contact shields 32, 42, and cylindrical electrodes 33, 43.
The electrode 33 of the fixed electrode 30 is welded in order for a protrusion (not shown) of its front edge portion to be passed through the contact shield 32 and to be connected to the contact 31, and its rear edge portion is passed through the cover 20, and connected to a fixed terminal 34 connected to a power source(not shown) of a main circuit.
The electrode 43 of the movable electrode 40 is welded so that a protrusion (not shown) of its front edge portion can be passed through the contact shield 42 and connected to the contact 41. A bush 44 is provided to an outer surface of the electrode bar 43, passing through the cover 21. A rear edge portion of the electrode bar 43 is externally protruded through the bush 44, and connected to a link (not shown) connected to a trip mechanism (not shown).
A bellows 45 is provided to an outer surface of the bush 44. The bellows 45 is shrunken or relaxed according to movement of the movable electrode 43, and interrupts air entering through a gap between the electrode bar 43 and an inner wall of the bush 44, thereby maintaining the vacuum state of the insulated container 10.
FIGS. 2 and 3 are a plan view and a cross-sectional view respectively illustrating the contacts 31, 41. The contacts 31, 41 will now be explained in more detail.
The contacts 31, 41 respectively include a plane-shaped contact portion 60 which is side-connected in a turn-on state, and a slant surface 70 which is not connected. A groove 90 having a predetermined depth is formed at a center of the contact portion 60. A plurality of L-shaped slits 80 are formed from the contact unit 60 and the slant surface 70, thereby forming a windmill shape.
Reference numeral 50 depicts a fixed ring, and reference numerals 51, 52 and 53 depict shields for protecting adjacent components from the arc generated when the contacts 31, 41 are separated.
The operation of the conventional interrupter will now be described.
In a state where the contacts 31, 41 of the electrodes 30, 40 are connected, if the abnormal current flows from the fixed side to the movable side, or vise versa, the movable contact 41 is separated from the fixed contact 31 by the link connected to the trip mechanism operated by receiving a turn-off signal, and thus the arc is generated from the contact portion 60 of the contacts 31, 41.
Here, a magnetic field is formed around the arc due to the arc current flowing along the arc. This magnetic field is in a horizontal direction.
Accordingly, as the time lapses, the arc consecutively alternated with the horizontal magnetic field receives the Lorentz force, and moves from the contact portion 60 of the contacts 31, 41 to the slant surface 70, thereby preventing the contacts 31, 41 from being partially heated and damaged.
However, in the conventional contact, if the arc current flowing when the abnormal current is interrupted is over 8kA, the arc tends to be concentrated on a single point of the contact portion 60. The concentrated arc is also moved by the Lorentz force.
Therefore, a melting phenomenon takes place in the contact by the concentrated arc. Furthermore, a melting and hardening line is formed in the contact along the movement path of the concentrated arc, and thus the contact is damaged or melted and hardened.
As a result, it is impossible to use the conventional contact in order to interrupt the abnormal current over 40kA.